8 May 2014
Brown-headed cowbirds (Molothrus ater) are courting now because their victims are nesting. The males sing a bubbly whistling song to attract a favored female. After she’s chosen a mate, Mrs. Cowbird lays her eggs in the nests of smaller birds. Her victims raise her chick while their own eggs and nestlings die, partly at the hands of her aggressive cowbird chick.
Cowbirds never build nests nor do they incubate so their pair bond is cemented by courtship songs and postures. Amazingly, the quality of the male’s song really matters. That’s how the female decides who to accept and who to ignore.
What happens if a female can’t tell the difference between good and bad songs? What happens within the flock when one lady doesn’t follow the rules? Last year scientists learned that a single tone-deaf female can upset cowbird society.
Researchers at the University of Pennsylvania led by Sarah Maguire inactivated the song-control centers of some female cowbirds’ brains so they could no longer distinguish between high and low quality songs. When placed in a mixed-sex flock these ladies reacted to all songs and did not stay with a chosen male for long.
Since male dominance among cowbirds is based on song quality the best guys usually get the best gals. However, when a tone-deaf female appeared in the flock she listened to all males equally and the minor males got a boost. The dominant males courted the altered female more vigorously. The other ladies were left in the cold.
Which guy will she choose? One tone-deaf female can mess up an entire social structure.
Read more here in PLOS One.
(photo from Wikimedia Commons, Creative Commons license. Click on the image to see the original)
I’ve always thought so!
Off the subject of cow birds – but there was another article in the TribLive yesterday about the rat infestation in Hazelwood. County officials are going to try a new poison that extracts calcium from the bones of the rats and deposits in their organs. The article said the poison won’t affect the eagles because their hollow bones don’t store calcium in the same way. The full article is on the TribLive website.
I get groups of cow birds at my feeder at different times of the year. Once young birds fledge, do they then join up with other cow bird groups? I’m assuming they don’t stay with their “adopted” parents. I wonder how they know to repeat this behavior generation after generation, since the young birds live and grow up with other birds that don’t do this?
Susan, click here for the answer to “how cowbirds know they are cowbirds.”
very helpful! It’s the Stellaluna of birds.